In ocean fisheries, incidental catch (or bycatch) poses a deadly threat to sharks and rays. The long lines trailing hooks – sometimes numbering in the thousands – can float in the open sea, and when non-target species pass by, they are also vulnerable to it.
A research team’s new device could keep the Sharks and stingrays safe from bycatch by taking advantage of their sensitivity to electric fields. SharkGuard is a small cylindrical device that attaches to fishing lines just above the hook and emits a pulsating electric field at close range.
The bet is that sharks and rays can sense tiny electric fields through bulbous organs concentrated near their heads called Ampullae of Lorenzini. So when they meet the transmitter, the developers of SharkGuard said in the log Current biologyit likely “overstimulates” their systems and ideally deters them from hitting the hook.
But whether SharkGuard’s small pulses would repel or attract animals was an unknown at first. Sharks and pelagic rays use their heightened electrical perception when hunting to detect small electrical fields emitted by prey.
So the developers of the device had to carry out field tests. Marine biologist Rob Enever of Fishtek Marine, a conservation engineering company in England, sent two fishing vessels in the summer of 2021, ScienceNews reported. The searchers hooked both boats with normal and SharkGuard hooks, and the crews began fishing for tuna.
The tests on the SharkGuard device were relatively successful.
Hooks with the electric repellent reduced blue shark catch rates by 91% compared to standard hooks. Test boats also caught 71% fewer pelagic rays with SharkGuard.
In numbers, this represents an average reduction from 6.1 blue sharks caught per 1,000 hooks to just 0.5 sharks – and seven rays to two. For scale: the two boats deployed nearly 19,000 hooks in total between them during testing.
In total, each boat would have caught around 60 sharks and 70 rays with standard hooks, but only caught five sharks and 20 rays with SharkGuard.
Apply the numbers to the millions of commercial fishing vessels operating around the world and “you’re going to have a massive recovery of those pelagic shark populations.” Enever said.
The test video shows the effect of the device on blue sharks. Although the long term effects of electrical impulses on sharks are not yet known, it is a fact that trolling lines will certainly harm them.
SharkGuard probably won’t roll out at scale overnight. The device does not appear ready for commercial deployment, in part because tuna catches during testing were unusually low.
ScienceNews reported exceptionally low tuna catches “at all levels” in the study. This made it impossible for researchers to say whether SharkGuard also bothers tuna. If so, the deterrent to fishing operations is obvious.
Other problems also exist. The developers of the device are would have work to make it cheaper and easier to charge the batteries of the invention. Further testing involving more species of sharks and rays is also expected to take place and while the effects of SharkGuard appear promising, broader efforts to conserve the two species of ocean predators remain essential.
“We are now in a situation where many of our pelagic species are either critically endangered, endangered or vulnerable,” Enever said. said.
But, he added, SharkGuard is cause for optimism. “[T]here are people out there…trying to solve these problems. There is hope for the future.